1. Field of the Invention
The present invention relates generally to optical communications, and particularly to apparatus for and a method of routing individual channels, or sub-bands of channels, of at least one incoming wavelength-division-multiplexed (WDM) signal, each to one or more of outgoing signals selected from two or more, the outgoing signals being multiplexed signals or single-channel signals as required.
2. Technical Background
Efficient management of high-capacity WDM optical communications networks requires routing apparatus (known as add-drop units or filters) that are “tunable” to select any one, or more than one, of the channels making up the signal, and extract it, or them, individually or in subgroups, for direction to a desired destination. An important application of such apparatus is at the node where a local loop is connected to a metropolitan loop, where it serves to select the particular channels (or subgroups) to serve the local loop. If possible, such apparatus should be capable of very rapid route-switching; it must maintain signal levels and if possible equalize or otherwise balance them between the various channels.